1. Field of the Invention
The present invention relates to oil well servicing and more particularly to a method and apparatus for removal of accumulated substances including paraffin deposits along an oil well tubing, and more particularly to such methods and apparatuses that do not require power through a wireline.
2. Prior Art and Background
Petroleum crude oil contains many constituents that can precipitate from the crude as it moves from the producing formation to the wellhead. One of those constituents is paraffin. The accumulation of paraffin within the production tubing of a working oil well is a major problem experienced throughout the petroleum industry. While the paraffin content of crude oil is variable, virtually all petroleum contains some paraffin that can result in the solidification of paraffin within the production tubing as the produced fluids travel from a downhole producing zone to the surface termination of the production tubing at a wellhead. As the buildup of solidified paraffin along the production tubing progresses, the ability to produce fluids through the tubing diminishes and eventually, in the worst case, the production tubing may become plugged to the point of preventing any flow of fluids. Plugging of the production tubing with substances found in the produced fluids, including paraffin deposits, requires servicing of the well for removal of the deposits before production of fluids can be resumed.
While paraffin may occur in most petroleum crude oil, the paraffin in each crude oil may have different characteristics and, in particular, may have a different melting temperature (or cloud point temperature). The temperature and pressure conditions will change along the passage of fluids from the producing zone within the formation through production tubing and the paraffin may solidify on the production tubing as the fluid cools in its path to the wellhead.
For example, a typical oil well temperature profile may show a temperature of 200° F. at 12,000 feet of depth within the well, a temperature of 170° F. at 7,000 feet of depth and a continued temperature reduction to the wellhead. If the produced fluids passing upward through the tubing in such a well contains paraffin having a cloud point lower than 170° F., it becomes possible for paraffin deposits to accumulate along the inner wall of the tubing at any location where the temperature is lower than 170° F. Continued accumulation of deposits could cause the well tubing to become blocked.
Many alternatives have been proposed for the prevention of paraffin buildup or the removal of paraffin deposits from production tubing including mechanical, chemical and electrical systems to keep the paraffin buildup from interfering with the production of fluids through the production tubing. Some of the alternative proposals are permanent installations within the producing well, while others are proposals for a servicing apparatus that is inserted through the wellhead and lowered to the tubing position needing servicing. Most well servicing tools or apparatus are tethered on a wire line, a tubing or a rod that lowers the tool through the wellhead to the servicing location cleaning the interior of the production tubing as the tool is lowered into the well or as the tool is raised to the wellhead. In the case of paraffin removal tools which employ heating elements, the wireline provides electrical power to the tool for raising the heating element temperature to a level required to melt the paraffin.
Petroleum wells may have well casing and production tubing within the casing and, in some wells, the production tubing may further include other tubings or rods that are inserted within the production tubing. When a plugged well tubing is serviced, some of the tubings within the production tubing must be removed to permit the entry of servicing tool. The process of removing tubing from a well bore, the insertion of a servicing tool and return of the tubing to put the well back into production is both time consuming and expensive. Most well servicing requires the use of well servicing rig or service company and an interruption of production through the well as the rig is put into place and a servicing tool is run into and out of the well.
In light of the foregoing background information, it has become apparent that there is a need for a method and apparatus for providing inexpensive and dependable removal of paraffin buildup along the interior of production tubing in a petroleum well. Further, it would be desirable to provide an apparatus that may be placed into a well tubing without the need of a servicing rig and without the need for extended interruption of production from the well. Moreover, it would be desirable to provide an apparatus that operates from onboard battery power, avoiding the requirement for electrical power from a wireline. An apparatus capable of the foregoing would have to overcome a number of challenges, including: (1) potentially long resident times downhole for the paraffin melting tool; (2) high temperatures for the heating element required to quickly and consistently melt the paraffin; (3) high power output from the batteries to continuously generate the required temperatures in the heating element; (4) battery management technology that can balance the required power output with maximum operating times downhole; and (5) a very narrow environment in the well tubing, which imposes significant design constraints. It is believed that the present invention addresses all of these challenges, and that it provides a new and innovative method and apparatus to remove paraffin deposits.